1. Field of the Invention
The present invention relates to an image quality adjustment technique for adjusting picture quality of image data.
2. Description of the Related Art
The picture quality of image data generated by a digital still camera (DSC), digital video camera (DVC) or the like can be adjusted as desired using an image retouching application on a personal computer. An image retouching application is typically equipped with a picture quality adjusting function for automatically adjusting picture quality of image data; by using this picture quality adjusting function, the picture quality of an image output by an output device can be improved. CRTs, LCDs, printers, projectors, and television receivers, for example, are known as image output devices.
A printer driver, which controls the operation of one of these output devices, namely, a printer, is also equipped with a function for automatically adjusting picture quality, and the quality of printed images can be improved using such a printer driver as well.
However, the automatic picture quality adjusting functions provided by image retouching applications or printer drivers execute quality correction based on image data deemed to have typical standard image characteristics. On the other hand, the image data being subjected to image processing may have been produced under various conditions, so in some instances quality will not be improved by executing a single standardized automatic picture quality adjusting function.
The light source providing illumination of a subject may be selected according to shooting location, time of day, and user preference from among various sources such as natural light sources (e.g. sunlight) or artificial light sources (e.g. fluorescent or incandescent lighting, or candlelight). The spectral distribution of light is different for different light sources. Thus, for a given subject, images of unnatural color (color shift) may occur with light sources of different types. For example, where a light source contains intense red light, such as candlelight, images may appear reddish. The extent of color deviation is termed “color balance.” Since adjustment of color deviation is frequently performed with reference to a white image area that is substantially achromatic, it is also referred to as “white balance.”
In image generating devices as well, various operating settings may be selected according to user preference or type of subject. For example, when photographing a person under sunny skies, forced flash may be used in some instance in order to reduce shadowing on the face, even where the subject is bright overall.
Where picture quality correction based on image data deemed to have typical picture quality characteristics is performed on images produced with different image generating device operating settings, or color shifted images, it will not be possible in some instances to improve overall image picture quality. This problem is not limited to DSCs, and is shared by DVCs and other such image generating devices.